ABSTRACT This is a revised application in response to the PAR-15-359, entitled ?Novel Approaches to Diagnosing Alzheimer's Disease & Predicting Progression (R01)?. Alzheimer's disease (AD) is the most common dementia in the elderly population and one of the leading causes of death in the developed world. One of the main problems in AD is the lack of an early, sensitive and objective laboratory diagnosis to identify individuals that will develop the disease before substantial brain damage. Compelling evidences point that the hallmark event in AD is the misfolding, oligomerization and brain accumulation of protein aggregates. Similar to AD several other neurodegenerative disorders are associated to the accumulation of cerebral protein aggregates, including Parkinson disease (PD), amyotrophic lateral sclerosis, prion diseases, and Huntington disease. In AD the most abundant protein aggregates are amyloid plaques and neurofibrillary tangles composed of the amyloid-beta (A?) and Tau proteins, respectively. Although the protein involved in the misfolding and aggregation process is different in each disease, the end products and intermediate structures are very similar. Moreover, in all cases, protein misfolding and aggregation follows a seeding-nucleation mechanism in which the limiting step is the formation of small oligomeric intermediates that act as seeds to catalyze the polymerization process. Recent evidence has shown that misfolded oligomers are circulating in biological fluids and these structures appear to be key for inducing brain degeneration. Our working hypothesis is that a sensitive, comprehensive and early biochemical diagnosis of AD may be developed by ultra-sensitive and simultaneous detection of misfolded oligomers composed of the three most common protein aggregating in the human brain (A?, Tau, and ?Syn) in human biological fluids (CSF and blood plasma). Our approach for detection of these oligomers is to use the functional property of misfolded oligomers of being capable to catalyze the polymerization of the monomeric protein as a way to detect them. For this purpose, we invented the protein misfolding cyclic amplification (PMCA), which represents a platform technology to detect very small quantities of seeding-competent misfolded oligomeric proteins associated with various protein misfolding diseases. Currently, PMCA has been adapted to detect misfolded prion protein implicated in prion diseases in various biological fluids, including blood and urine and more recently soluble A? and ?Syn oligomers in CSF of AD and PD patients, respectively. The major goal of this project is to adapt the PMCA technology for specific and highly sensitive detection of misfolded A?, Tau, and ?Syn oligomers in human blood and CSF in order to obtain a fingerprint profile that enable to diagnose AD and distinguish from other diseases with similar clinical presentation. In this project we will perform studies of specificity and sensitivity using large number of samples and evaluate the utility of PMCA for monitoring disease progression and for pre-clinical identification of people in the way to develop AD. The results generated in this project may lead to the development of a comprehensive biochemical test for AD that may be useful not only to aid in the diagnosis of the disease and differentiate it from other diseases with similar clinical presentation, but also to identify people on the way to developing AD pathology before the onset of substantial brain damage and clinical symptoms of the disease.